299T and Hama (?) optical slave trigger device

greenspun.com : LUSENET : Canon FD : One Thread

I have tried to use the Canon 299T flash (trigger voltage about 5 Volts) with a simple sync cable adapter and HAMA optical slave device.

It seems to trigger fine but only once. If I remove the slave device and reconnect it it fires again but only once. My other older flash with trigger voltage around 200V works fine.

Any advice what to do, except: 1) return the slave device and use sync cable or 2) use another flash.


-- Vesa Perala (vpera@hotmail.com), February 22, 2000


It was ROWI, not Hama. Sorry.

-- Vesa (vpera@hotmail.com), February 22, 2000.

I suspect the 299T requires a high trigger current and thus prevents the slave from resetting.

Long explanation: AFAIK a slave contains something called an LASCR (light activated silicon controlled rectifier). Under the influence of light from the primary strobe the LASCR turns on and acts as switch that triggers the 299T. The LASCR will stay on even when the flash is over if the 299T provides sufficient current. Disconnecting the slave stops the current and the slave resets. This does no damage.

You might try this:

1.) try another optical slave device; it may just be the combination of slave and flash. The second slave may be immune to the high trigger current.

2.) if you have access to electronic components such as resistors and capacitors you might try the following:

a.) put a resistor from the trigger pin to the common pin to divert some current from the slave. The value of the resistor should be on the order of 500 ohms to 1000 ohms. If the resistor is too high it will not solve the problem. If it is too low the 299T will not trigger at all.

b.) put a resistor in parallel with a capacitor and the combination in series with the trigger wire. Unfortunately you will have to cut the trigger wire. The resistor should have a value of 1000 ohms and the capacitor a value of 100 uF at 6 volts or greater. The + of the capacitor should connect to the 299T. The resistor will reduce the current while the capacitor will allow a higher current to flow only during the trigger.

If you have any questions, feel free to ask.



-- Duane K (dkucheran@creo.com), February 28, 2000.

I have a Hama slave trigger, and have the same problem with my 577G, but not with my 300TL. I will not try the suggested thing, but maybe read better the next time I buy something.

-- Cyvind Dahle (odahle@start.no), October 27, 2000.

Moderation questions? read the FAQ